Toughening of epoxy hybrid nanocomposites modified with silica nanoparticles and epoxidized natural rubber

Silica nanoparticles (SN) and epoxidized natural rubber (ENR) were used as binary component fillers in toughening diglycidyl ether of bisphenol A (DGEBA) cured cycloaliphatic polyamine. For a single component filler system, the addition of ENR resulted in significantly improved fracture toughness (K_IC) but reduction of glass transition temperature (T_g) and modulus of epoxy resins. On the other hand, the addition of SN resulted in a modest increase in toughness and T_g but significant improvement in modulus. Combining and balancing both fillers in hybrid ENR/SN/epoxy systems exhibited improvements in the Young’s modulus and T_g, and most importantly the K_IC, which can be explained by synergistic impact from the inherent characteristics associated with each filler. The highest K_IC was achieved with addition of small amounts of SN (5 wt.%) to the epoxy containing 5–7.5 wt.% ENR, where the K_IC was distinctly higher than with the epoxy containing ENR alone at the same total filler content. Evidence through scanning electron microscopy (SEM) and transmission optical microscopy (TOM) revealed that cavitation of rubber particles with matrix shear yielding and particle debonding with subsequent void growth of silica nanoparticles were the main toughening mechanisms for the toughness improvements for epoxy. The fracture toughness enhancement for hybrid nanocomposites involved an increase in damage zone size in epoxy matrix due to the presence of ENR and SN, which led to dissipating more energy near the crack-tip region.     

Pineapple leaf fibers (PALF) as the sustainable carbon anode material for lithium-ion batteries

Journal of Materials Science: Materials in Electronics - Pineapple leaf fiber (PALF) is considered as a promising low cost carbon precursor to produce a high graphitic carbon material, regarding to...     

Effect of silica nanoparticle size on toughening mechanisms of filled epoxy

The addition of silica nanoparticles (23 nm, 74 nm, and 170 nm) to a lightly crosslinked, model epoxy resin, was studied. The effect of silica nanoparticle content and particle size on glass transition temperature (T_g), coefficient of thermal expansion (CTE), Young's modulus (E), yield stress (σ), fracture energy (G_IC) and fracture toughness (K_IC), were investigated. The toughening mechanisms were determined using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and transmission optical microscopy (TOM). The experimental results revealed that the addition of silica nanoparticles did not have a significant effect on T_g or the yield stress of epoxy resin, i.e. the yield stress and T_g remained constant regardless of silica nanoparticle size. As expected, the addition of silica nanoparticles had a significant impact on CTE, modulus and fracture toughness. The CTE values of nanosilica-filled epoxies were found to decrease with increasing silica nanoparticle content, which can be attributed to the much lower CTE of the silica nanoparticles. Interestingly, the decreases in CTE showed strong particle size dependence. The Young's modulus was also found to significantly improve with addition of silica nanoparticles and increase with increasing filler content. However, the particle size did not exhibit any effect on the Young's modulus. Finally, the fracture toughness and fracture energy showed significant improvements with the addition of silica nanoparticles, and increased with increasing filler content. The effect of particle size on fracture toughness was negligible. Observation of the fracture surfaces using SEM and TOM showed evidence of debonding of silica nanoparticles, matrix void growth, and matrix shear banding, which are credited for the increases in toughness for nanosilica-filled epoxy systems. Shear banding mechanism was the dominant mechanism while the particle debonding and plastic void growth were the minor mechanisms.     

Impacts of spray drying conditions on stability of isoflavones in microencapsulated soybean extract

Abstract

Soybean extract rich in isoflavones has attracted widespread attention for dietary supplement and pharmaceutical purposes. However, it has poor solubility and low stability. Encapsulation using spray drying is a good alternative for overcoming these problems in soybean extract. Isoflavones profiles in soybean extract are altered during encapsulation and storage. The objective of this work was to investigate the effect of spray drying conditions on the isoflavones profiles and the various properties of microencapsulated soybean extract. The studied parameters comprised the type of wall material (maltodextrin [MD], gum arabic [GA], and β-cyclodextrin [βCD]), inlet air temperature (130–170?°C) and storage time (0–6?months), while the investigated properties included moisture content, particle size, hygroscopicity, morphology, isoflavones content, encapsulation properties, and Fourier transform infrared analysis. Type of wall material had a more significant impact on the properties of microencapsulated soybean extract than inlet air temperature. The degradation of total isoflavones during storage mainly depended on the inter-conversion level of isoflavones during encapsulation, hygroscopicity and heating history of microencapsulated soybean extract. The use of βCD as wall material could preserve total isoflavones after encapsulation and storage at 0.1–1.3 and 2.4–3.1 times that in the case of MD and 1.1–1.3 and 1.5–1.8 times that in the case of GA, respectively. Abbreviations AI aglycone isoflavones (daidzein and genistein)

AGI acetyl β-glucoside isoflavones (6″-O-acetyldaidzin and 6″-O-acetylgenistin)

βCD β-cyclodextrin

GA gum arabic

GI β-glucoside isoflavones (daidzin and genistin)

MD maltodextrin

MGI malonyl β-glucoside isoflavones (6″-O-malonyldaidzin and 6″-O-malonylgenistin)

SE soybean extract

SE-βCD microencapsulated soybean extract using β-cyclodextrin as wall material

SE-GA microencapsulated soybean extract using gum arabic as wall material

SE-MD microencapsulated soybean extract using maltodextrin as wall material

TI total isoflavones (sum of MGI, AGI, GI and AI)